1. Field of the Invention
The present invention relates to a semiconductor element that has a lateral structure, and especially to a semiconductor element, which is small in size, that has a lateral structure.
2. Description of the Related Art
In an analog integrated circuit, a lateral PNP transistor that has a structure where an emitter region, a collector region, and a base region are formed adjacent in a horizontal direction, is used. As shown in the plane view in FIG. 7, the semiconductor element used in the lateral PNP transistor is constituted by an N−-type base region 33, a P+-type collector region 34, a P+-type emitter region 35, an N+-type base contact region 36, and a P+-type isolation region 38. When a current is passed through a semiconductor element (transistor) that has this kind of structure, the current from the emitter region 35 not only flows towards the collector region 34, but as shown by arrows YB, also flows towards the base contact region 36 and the isolation region 38. By such diffusion of current, a leakage current generates at the operation time of the transistor. As a result, the current amplification factor of the transistor drops. So, in order to prevent the leakage current from generating, a lateral PNP transistor where the vicinity of the emitter region 35 is surrounded by the collector region 34 is proposed. This kind of lateral PNP transistor is disclosed in for example, FIG. 1 of Unexamined Japanese Patent Application KOKAI Publication No. H10-270458.
FIG. 8 is a plane view of a semiconductor element that has a structure where a collector region surrounds an emitter region. FIG. 9 is a cross-sectional view in line C–C′ in FIG. 8. As shown in FIGS. 8 and 9, a collector region 44 is formed so as to surround an emitter region 45, separated a predetermined distance from the emitter region 45. Therefore, as shown by arrows YC, most of the current that flows from the emitter region 45, flows to the collector region 44. By this, generation of the leakage current at the operation time of the transistor, is prevented.
However, because the collector region 44 is formed so as to surround the emitter region 45, the area of the collector region 44 inevitably becomes larger. Accompanying this, the area of the entire semiconductor element also becomes larger. Consequently, making the size of the semiconductor element smaller, is considered by narrowing the interval WB (base width WB) between the collector region 44 and the emitter region 45. To maintain the high withstand voltage of the transistor, the base width WB must be kept equal to or wider than a certain width. Therefore, there is a limit in miniaturizing the size of the semiconductor element. Consequently, it is difficult to obtain a semiconductor element of a requested size, with a semiconductor element having a structure where the collector region 44 surrounds the emitter region 45.
The content of the above document is incorporate herein by reference in their entirety.